Thermal relay for electric discharge lamps



Dec. l5, 1942. H. J. MCC'ARTHY THERMAL RELAY FOR ELECTRIC DISCHARGE LAMPS Filed March 22, 1941 A Foie/vf Y fg 4 Y H 91171)? j MCCILTyJNVENTOR. BY

Patented Dec. 15, 1942 THERMAL RELAY FOR ELECTRIC DISCHARGE LAMPS Henry I. McCarthy, Danvers, Mass., assignor to Sylvania Electric Products inc., a corporation of Massachusetts Application March 22, 1941,*-Seria1 No. 384,721

(Cl. 21m-122) l Claims.

This invention relates to electric gaseous discharge lamps and more particularly to VVthermal relays therefor.

An object of this invention is to provide a thermal relay which will allow the cathodes of the iamp to be preheated before the discharge between them starts.

Another object is to provide a thermal relay in which the contacts may-be located very close together yet arranged in a manner to insure the proper spacing at all times.

A further object isto provide a thermal relay in which the above features will be embodied and at the same time be of simple construction.

Other objects, advantages and features will be apparent from the following specification taken in conjunction with the accompanying drawing in which:

Figure 1 is a projection of the thermal relay;

Figure 2 is a detail in section thereof;

Figure 3 is a schematic diagram of the circuit in the relay;

Figure 4 is a projection of a simpler construction of my thermal relay.

Similar reference characters refer to similar parts in the several views of the drawing and in the specification which follows.

The relay in my invention comprises a resistance rod supported between and connected to the two lead-in wires, two concentric bimetallic strips bent around the resistance rod and two contacts, one on each free end of the two bimetallic strips.

In Figure 1, the resistance rod l is suspended between the two lead-in wires 2 and 3. Attached to the wire 2 is the arm 4 to which is fixed one end of the inner bimetallic strip i. Attached to the wire 3 is the' arm 6 to which is xed one end of the outer bimetallic strip 1. The contact B is located on the free end of the inner strip 5, while the contact 9 is located on the free end of the outer strip 1. The manner in which the relay operates may be better understood by a description thereof in conjunction with Figure 2. Y The resistance rod I is provided with an insulating coating, as shown in Figure 2. I have found that a coating of alumina and shellac is suitable. I apply two coats of a dewaxed shellac and then two coats yof an alumina-shellac mixture. The shellac' coats y are denoted by the numeral lil while the coats of alumina-shellac y mixture are denoted by the numeral Il. Although I have used two coats of shellac and two coats of alumina-shellac, the number o f coats may be varied inasmuch as uniformity of the alumina shellac mixture because with lthe shellac foundation a higher break-down voltage is obtained. This coating also prevents the bimetallic strip :from cutting through the resistance rod.

In Figure 2, when the line voltage is initially placed across the resistance rod i, the inner birnetallic strip 5 will become heated first because this strip is actually in contact with the coating on the resistance rod l. As 'the strip becomes heated, it will bend towards strip i until contact B at the free end of strip 5 touches contact 9 on the free end of strip 1. This-closes the circuit through the relay and as a result, the filaments of thelamp start to heat up.

Since the strip 5 acts as a shield between the source of heat, the resistance rod l, arid the strip 1, the strip i will not loegin to heat up until heat is radiated thereto from the strip 5. No appreciable amount of heat is radiated -to the strip l until after the contacts t and 9 have closed the circuit. Thus the strip t is starting to cool and bend back towards its initial position while the heat radiated therefrom is causing the strip 7 to bend away from its initial position. Thus, between the time the vcoiritaots close and the time they open again, the strip 5 is moving in one direction and the strip l in another direction. A clean, quick, and positive breaking away of the contacts 8 and 9 is thus insured. The time it takes for the circuit to open after having once been closed may be timed to coincide with the length of time necessary to preheat the iilaments of an electric gaseous discharge lamp sumcientiy to enable them to carry the discharge across the lamp. l

When the contacts break and the discharge across the lamp'starts, the voltage drop across the resistance rod will not he great enough to cause the contacts d and d to touch. After the voltage drop across the resistance has settled down to a substantially constant value, the strips 5 and 'l will be heated to about the same degree and therefore they will be distorted in the same direction to substantially the same extent. Thus they will remain substantially parallel and hence there will be novdanger of the contacts 8 and 9 touching each other while the lamp is running.

Figure 4 shows a more simple construction of my thermal relay. In this ligure the bimetallic strips I2 and I3 are joined together at one end. 'Ihe inner strip I3 is actually in contact with the resistance rod I4 suspended between the lead-in wires I5 and IG. f I'he contact Il is attached to the free end of the inner strip I3. The contact I8 is fixed on the end of the arm I5 extending in from the lead-in wire I6. These two joined bimetallic strips I2 and I3 which are concentric with the resistance rod Il are connected to the lead-in wire I5 through the arm 2l attached to the free endy of the outer bimetallic strip I2.

What I claim is:

1. A thermal relay for electric gaseous discharge lamps comprising: twolead-in wires; a resistance rod suspended therebetween; an insulating coating on said rod; two concentric bimetallic strips in position to be heated by said resistance rod, said strips being substantially parallel to each other along substantially the entire longitudinal axis thereof; and two normally open electrical contacts on the free ends of said bimetallic strips.

2. A thermal relay comprising: two lead-in wires; a resistance rodA suspended therebetween; two bimetallic strips concentrically wound around said resistance rod, said strips being substantially parallel to each other along substantially the entire longitudinal axis thereof, one of said strips being in contact with said resistance rod; and two normally open electrical contacts on the free ends of said bimetallic strips.

3. A thermal relay comprising: two lead-in wires; a resistance rod suspended therebetween; an insulating coating on said rod; two bimetallic 'strips concentrically wound around said rod,

resistance rod, one only of said strips being in contact with said coating on said rod; an electrical contact on the free end of one of said strips; and a second electrical contact on the free end of the other of said strips and normally open with respect to said first electrical contact.

5. A thermal relay for electricv gaseous discharge lamps comprising: vtwo lead-in wires; a resistance rod suspended therebetween; an insulating coating on said rod i two bimetallic strips normally substantially parallel to each other along substantially the entire longitudinal axis thereof wound concentrically around said resistance rod, one of said strips being in contact with said coating on said rod; an electrical contact on the free end of the strip which is'in contact with the coating on the resistance rod; and a second electrical contact normally open with respect to said ilrst electrical contact.

6. A thermal relay for preheating the filamentary electrodes of an electric gaseous discharge lamp comprising: two lead-in wires; a resistance rod suspended therebetween, a coating of an alumina and shellac mixture on said resistance rod; a pair of concentric bimetallic strips normally substantially parallel to each other along substantially the entire longitudinal axis thereof suspended from said lead-in wires and extending around said resistance rod, one of said strips being in contact with the coating on said rod; and two electrical contacts, one on each of the free ends of said bimetallic strips and in contact relationship with each other.

7. A thermal relay for preheating the illamentary electrodes of an electric gaseous discharge lamp comprising: two lead-in wires; a resistance rod suspended therebetween; a coating oi' alumina and shellac mixture on said rod; a pair of concentric bimetallic strips normally substantially parallel to each other along substantially the entire longitudinal axis thereof attached to each other at one end, being suspended from one of the lead-in wires from the other end of the outer one of the two bimetallic strips; an electrical contact supported on an arm projecting inward from one of said lead-in wires; and a second electrical contact on the free end of the inner bimetallic strip in a position to be contacted by said rst mentioned contact.

HENRY J. MCCARTHY. 

